Hi Chris,
I'm using your module, however for any total order weights above 1.5KG, both the AirMail and Surface mail return "The shipping rate cannot be determined at this time". But for anything under that weight, it calculates the price. In the admin settings for the two shipping modules I've set the maximum weight to 100. And for the general store maximum weight is a high amount as well.
So what do you think would be cause of it not calculating the shipping for weights above that amount?
Thanks mate.